The invention disclosed herein relates generally to hard disk drive suspensions. More specifically, the invention relates to hard disk drive suspension assemblies and circuit assemblies with an integral flexible circuit and integral support member.
Suspension assemblies in hard disk drives include a head gimbal assembly (HGA). The HGA includes a gimbal assembly, a head assembly, and an interconnect assembly. The head assembly includes a highly sensitive read/write transducer, commonly referred to as a head, attached to an air bearing slider. The head assembly also includes electrical terminals configured for interconnection to the interconnect assembly for receiving and relaying data signals. The head assembly facilitates reading and writing of information on a surface of a rotating magnetic disk. The interconnect assembly includes a plurality of transmission elements, such as wires or traces, for transmitting data to and from the head assembly. The suspension assembly positions the head assembly at a generally constant distance away from the moving surface of the rotating disk. The suspension assembly permits the head assembly to xe2x80x9cflyxe2x80x9d at a height above the surface of the disk, including surface irregularities.
Most conventional suspension assemblies, also referred to herein as a support member, include a load beam and a gimbal portion. The load beam is a resilient spring plate designed to provide lateral stiffness. The load beam is calibrated to apply a force on the head assembly that counteracts a lift force on the head that is provided by the air stream generated by the rotating disk. Accordingly, the head assembly flies above the surface of the disk at a height established by the equilibrium of the load beam force and the lift force.
The gimbal portion is positioned adjacent to an end of the load beam and has the head assembly attached thereto. The gimbal portion permits roll and pitch deflections of the head assembly in response to flying over surface imperfections and warping of the rotating disk. By permitting these deflections, the gimbal portion aids in maintaining the proper orientation and distance of the head assembly relative to the rotating disk, even when the load beam exhibits a slight amount of flexing and twisting.
The suspension assembly can be attached at its proximal end to a rigid arm or directly to a linear or rotary motion actuator. The actuator rapidly moves and then abruptly stops the HGA over any position on a radius of the disk. The radial HGA movement and the rotation of the disk allow the head to quickly reach every location above the disk. However, the rapid stop and go movement causes very high stresses on the HGA.
An ideal HGA comprises components low in mass. Excessive inertial momentum caused by excessive mass can cause overshoot errors. Overshoot errors occur when momentum carries the whole HGA past the intended stopping point during positioning movement. Low-in-mass HGA""s are easier to move, resulting in power savings in multiple platter disk drives. Furthermore, lighter weight HGA""s permit the head to be flown closer to the surface of the disk. The closer the head assembly can fly to the surface of the disk, the more densely information can be stored on the disk. Accordingly, a lightweight HGA is desirable in high performance disk drives.
It is known that the strength of a magnetic field in a disk drive varies proportionally to the square of the fly height of the head. Manufacturers of disk drives strive to reach flying clearances less than 100 nanometers, which is 0.1 micrometers. For comparison, a human hair is about 100 micrometers thick. However, the head assembly must not touch the disk, since the impact with the spinning disk, which rotates at about 10,000 rpm or faster, can damage the head and the surface of the disk.
Amplifying and control circuits process, send and receive the data signals to and from the head assembly. Signal transmission requires conductors to extend between the head assembly and the related circuitry of the disk drive. Traditional head assemblies use a read-write circuit loop with two conductors, usually copper wires encapsulated in plastic sheeting. Newer types of magnetic read-write heads, commonly referred to as magneto-resistance head assemblies, require four or more independent conductors.
The increasing need for more wires, lower disk stack height and less stiffness and mass of the suspension assembly has forced the manufacturers to consider different suspension design approaches. In one design approach, a suspension assembly has signal traces that are etched from a stainless steel based material and an insulating layer is subsequently formed over the signal traces. The stainless steel base material is also etched to form the load beam portion and head gimbal portion of the suspension. A key limitation of this type of construction is excessive yield rates due to the integrated fabrication process and poor conductivity of stainless steel. In another design approach, a conventional flex circuit is attached to a separately fabricated suspension assembly using an adhesive. A key drawback with this type of construction is the cost associated with the precision required for assembling the flexible circuit to the suspension assembly.
Designers and manufacturers of HGA""s face competing and limiting design considerations. During operation, the suspension assembly should be free of unpredictable loads and biases which alter the exact positioning of the head assembly. The suspension assembly should respond instantaneously to variations in the surface topology of a disk. Alterations to the flying height of the head can significantly affect data density and accuracy and even destroy data stored on the disk if the head collides with the surface of the disk.
The rigidity and stiffness of a load beam increase in relation to the cross-sectional thickness by the third power. To respond to air stream changes and to hold the flying head at the appropriate orientation, suspension assemblies are very thin and flexible, especially around a sensitive spring portion of the load beam. Interconnect assembly conductors have a large effect on the performance of the suspension assembly. Conductor stiffness alone greatly affects the rigidity of the spring regions and flight performance.
A standard wire conductor attached atop the suspension can more than double the stiffness of a load beam and significantly limit the ability of the load beam to adjust to variations in the surface of the disk, vibrations, and movement. The effect of the conductors on a gimbal region, the thinnest and most delicate spring in the suspension assembly, is even more pronounced. Furthermore, conductors placed over spring regions of the load beam and gimbal portion of the suspension assembly must not plastically deform when the spring regions flex. Plastic deformation prevents the return of the load beam or gimbal portion to its normal position and applies a biased load on the suspension assembly.
In HGA""s that use conventional wire interconnect assemblies, two to five lengths of wire to the head assembly are manually connected to the head. Fixtures are used to manage the wires while they are being bonded to the head assembly. The lengths of wire are manually shaped using tweezers and tooling assistance to form a service loop between the head assembly and the suspension assembly and to position the wire along a predetermined wire path on the suspension assembly. The wires are tacked to the suspension using an adhesive or wire capture features formed into the suspension.
Special care is taken to avoid pulling the service loop too tight or leaving it too loose. A tight service loop places an unwanted torque on the head assembly causing errors associated with the fly height. A loose service loop allows the wire to sag down and scrape the adjacent spinning disk. Both conditions are catastrophic to disk drive performance.
Throughout the process of handling the head assembly, interconnect assembly and the suspension assembly, there is a risk of damaging the wires or the delicate load beam and gimbal. Load beams or gimbals accidentally bent during the manufacturing operations are scrapped. Often the head assembly also cannot be recovered, adding additional financial losses.
Similar to conventional wire interconnect assemblies, flexible circuit interconnect assemblies may inadvertently impart unbalanced or excessive forces on the suspension. Many common flexible circuit case substrates are also hydroscopic, resulting in flexural characteristics that are dependent on moisture content and humidity. Because the flexible circuits are formed separately from the suspension and subsequently attached, precision manufacturing tolerances are difficult and costly to maintain.
Therefore, what is needed is a circuit assembly for a disk drive head suspension that provides improved fly height control, that reduces noise in signal transmission to and from the head assembly, and that can be cost effectively manufactured.
Accordingly, in one embodiment of the present invention, a circuit assembly includes a base member and a plurality of traces formed directly on a first surface of the base member. The traces extend between a first end and a second end of the base member. A reference voltage member is formed directly on a second surface of the base member. The plurality of traces is positioned to overlay at least a portion of the reference voltage member. A support member is formed directly on at least a portion of the reference voltage member.
The support member is formed from a material exhibiting a tensile strength substantially greater than the tensile strength exhibited by the reference voltage member and the traces. A preferred material for the support member is a nickel alloy such as nickel boron or nickel-phosphorus or any suitable plateable material. A preferred material for the traces is copper, gold, palladium, tin, or any suitable plateable. In a preferred embodiment, the traces and the reference voltage member are formed of the same material.
The support member is preferably formed directly on the reference voltage member using an electroless plating process. The electroless plating process is preferably an autocatalytic electroless plating process. The use of an electroless plating process contributes to providing a support member with uniform thickness and allows the support member to be made from a preferred selection of materials.
The support member may be formed to have regions of different thickness as well as regions that are completely isolated from adjacent regions thereof. A load beam portion of the support member preferably has a thickness substantially greater than a gimbal portion thereof. The load beam portion of the support member may include spaced-apart flange portions having a main portion extending therebetween. The flange portion of the support member has a thickness substantially greater than the main portion of the support member.
Circuit assemblies and suspension assemblies according to the present invention exhibit an impedance value of less than about 200 ohms between any two traces.
In another embodiment of the present invention, a process for making a circuit assembly includes the steps of forming a plurality of traces directly on a first surface of a base member, wherein the traces extend between a first end and a second end of the base member; forming a reference voltage layer directly on a second surface of the base member, wherein the plurality of traces overlay at least a portion of the reference voltage layer; and forming a support member directly on at least a portion of the reference voltage layer.
In a further embodiment of the present invention, a disk drive suspension assembly includes an elongated polymeric base member having a plurality of traces formed directly on a first surface thereof and a reference voltage member formed on a second surface thereof. A support member is formed directly on at least a portion of the reference voltage member. The plurality of traces overlay at least a portion of the reference voltage member. The reference voltage member is formed from a first electrically conductive material and the support member is formed from a second electrically conductive material. The first electrically conductive material provides substantially greater electrical conductivity and substantially lower tensile strength than the second electrically conductive material. The support member includes a head gimbal portion having a first thickness and a load beam portion having a second thickness. The second thickness is substantially greater than the first thickness.
The following terms have the following meanings when used herein:
1. The term xe2x80x9celectroless depositionxe2x80x9d refers to processes in which a layer of material is deposited onto a non-conductive substrate.
2. The term xe2x80x9celectroless platingxe2x80x9d refers to processes in which conductive features on a substrate are plated without being subjected to an externally applied current or voltage.
3. The term xe2x80x9cautocatalytic electroless platingxe2x80x9d refers to a process of depositing a metallic coating by a controlled chemical reduction where a reducing agent in the form of a chemical, such as sodium hypophosphite, provides the electrons.
4. The term xe2x80x9chead suspension assembly (HGA)xe2x80x9d refers to a structure including a gimbal assembly, a head assembly, and an interconnect assembly.
5. The term xe2x80x9csuspension assemblyxe2x80x9d refers to a structure including a load beam portion and a head gimbal portion.
6. The term xe2x80x9cload beamxe2x80x9d refers to a portion of the suspension assembly that provides a flexural-induced loading relative to a longitudinal axis thereof and that exhibits negligible torsional deflection relative to the longitudinal axis.
7. The term xe2x80x9cgimbal portionxe2x80x9d refers to a portion of the suspension assembly that permits pitch and roll movement of the slider.
8. The term xe2x80x9csupport memberxe2x80x9d refers to a structural member including the load beam and optionally including a gimbal portion.
9. The terms xe2x80x9csliderxe2x80x9d and xe2x80x9cheadxe2x80x9d are used interchangeably herein and refer to a unit for reading and writing information in a magnetic format, optical format or other type of data storage format.
10. The term xe2x80x9creference voltage layerxe2x80x9d refers to a layer of electrically conductive material that is spaced away from an adjacent electrical feature by a uniform distance.